1. Field of the Invention
The present invention relates to a fan having a fan motor and two signal lines including a number-of-rotations switching control signal line and a rotational state outputting signal line, in which the fan motor runs at a number of rotations determined by a number-of-rotations switching control signal input via the number-of-rotations switching control signal line, and the fan outputs the rotational state of the fan motor via the rotational state outputting signal line.
2. Description of the Related Art
Various fans have been used for ventilation or air conditioning (see Japanese Patent Laid-Open No. 5-252784 and Japanese Patent Laid-Open No. 5-264080, for example).
For example, a server has many fans for cooling. To prevent a failure of a fan from leading to insufficient cooling of the system and interruption of the service, such a server has a redundant configuration including more fans than necessary or unitizes the fans to enable active replacement. Furthermore, there is a system that monitors and controls fans and, if a fan fails, immediately notifies the system manager of the failure to permit replacement of the failed fan. A larger server requires more fans, so that each fan has to be monitored and controlled more precisely.
Most fans used for cooling servers have a number-of-rotations switching control signal line and a rotational state outputting signal line.
Such a fan outputs the rotational state of the fan motor, and thus, the system can monitor the rotational state to know if the fan motor runs normally at that instant. However, conventional fans provide no detail data as to the manufacturers, the dates of manufacture, when the fans were put into service, or how long the fans have been in service. Therefore, there is a problem that preventive measures cannot be taken, for example, a fan cannot be replaced with a new one based on a prediction that the fan will stop rotating soon.
Besides, there has been devised a system that unitizes fans and can grasp the performance of the fans by reading additional information, such as a switch-based ID setting (for example, four kinds of outputs represented by two bits), that is set in the unit for differentiating the fans according to their performance. However, additional signal lines for reading the switch-based ID setting have to be provided in the unit, and if multiple IDs are set, the number of signal lines increases. For example, a large server has many fans, and each fan has the number-of-rotations switching control signal line and the rotational state outputting signal line. Thus, such a further increase of the number of signal lines is a problem.
Alternatively, rather than simply setting an ID in the fan unit, a memory for storing detail data regarding the fans may be provided in the fan unit. However, if signal lines are provided for reading the data from the memory, for the same reason as described above, there arises a problem that the total number of signal lines extremely increases.